Microscopic Insight into Structure Determination of Ferroelectric Photovoltaics in Aurivillius-Phase Ferroelectrics

Recently, a high open-circuit voltage of the ferroelectric photovoltaic effect driven by the polar order of the ferroelectrics has been intensively reported in the Aurivillius-phase perovskite structure. However, the factors limiting the ferroelectric photovoltaic effect are not clearly understood. Here, we observed a correlation between the polar phase fraction and ferroelectric photovoltage in Sr1–xBaxBi4Ti4O15polycrystalline films, where the output intensity was regulated by the change in the phase fraction parameter ξ (I41am/A21amtetragonal–orthogonal phase), and lattice distortion was caused by the different dopant concentrations in the range of (x= 0, 0.2, 0.5, 0.8, and 1.0). The ferroelectric photovoltaic effect is outstanding in the SrBi4Ti4O15films, which confirms that the polar phase fraction plays a crucial role in the photocurrent intensity. The photovoltaic external efficiency can reach 28% at the spectrum response peak of 340 nm, and we also constructed a function relation to describe the intensity. These results indicate that the ferroelectric polarization and bandgap are significantly related to the phase fraction evolution. Further, our experimental results not only confirm the speculated mechanism of enhanced electron–hole separation in ferroelectrics but also clarify the unsymmetrical dispersion of photoelectrons as a key factor, which offers an opportunity to understand its nature.